rep clause confusion

rep clause confusion

[chris.danx]

Hi,

I've been looking at rep clauses(?), for laying seg descriptors for the x86,
and one thing confuses me.

for some_type
    use record
        abc        at 0 range 0..7;
        def        at 1 range 0..7;
    end record;

The 'at' bit confuses me.  Does this mean the storage element (numbered from
zero)?  If so that means, abc spans storage element zero bits 0..7 and def
spans storage element 1 bits 0..7.  Is this correct?


Happy New Year,
Chris

Re: rep clause confusion

[Ted Dennison]

In article <ed8Y7.27607$4x4.3341820@news2-win.server.ntlworld.com>, chris.danx
says...
>for some_type
>    use record
>        abc        at 0 range 0..7;
>        def        at 1 range 0..7;
>    end record;
>
>The 'at' bit confuses me.  Does this mean the storage element (numbered from
>zero)?  If so that means, abc spans storage element zero bits 0..7 and def
>spans storage element 1 bits 0..7.  Is this correct?

Yes. Think of them as offsets in storage elements (usually bytes) from the start
of the record.

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Re: rep clause confusion

[Jerry Petrey]

"chris.danx" wrote:
> 
> Hi,
> 
> I've been looking at rep clauses(?), for laying seg descriptors for the x86,
> and one thing confuses me.
> 
> for some_type
>     use record
>         abc        at 0 range 0..7;
>         def        at 1 range 0..7;
>     end record;
> 
> The 'at' bit confuses me.  Does this mean the storage element (numbered from
> zero)?  If so that means, abc spans storage element zero bits 0..7 and def
> spans storage element 1 bits 0..7.  Is this correct?
> 
> Happy New Year,
> Chris


Yes, the value after AT gives a storage unit (as defined in package System -
in this case, apparently a byte) and it can extend outside the storage unit.
You could have written the following with the same results:

 for some_type
     use record
         abc        at 0 range 0..7;
         def        at 0 range 8..15;
     end record;


Jerry

-- 
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-- Jerry Petrey                                                
-- Senior Principal Systems Engineer - Navigation, Guidance, & Control
-- Raytheon Missile Systems          - Member Team Ada & Team Forth
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